This is the mismatch met most often on international projects: metric DIN/EN flanges on one side, imperial ANSI/ASME flanges on the other.
The differences
| Criterion | ASME B16.5 (ANSI) | EN 1092-1 (DIN) |
|---|---|---|
| Measuring system | Inches, NPS | Metric, DN |
| Class designation | Class 150 – 2500 | PN 2.5 – PN 250 |
| Face raise | About 1.6 mm in 150#/300# | 2 mm in type B1 |
| Bolt thread | UNC / 8 UN | Metric ISO |
| Type designation | WN, SO, blind, LJ | Type 11, 01, 05, 02/04 |
Class equivalences are not one to one either. PN 16 and Class 150 look close, but their pressure temperature behaviour and bolt circles differ, so they cannot be treated as interchangeable.
Why they do not bolt together
Even at the same nominal size, bolt circle, bolt count and hole diameter differ. Forced solutions such as enlarging holes or adding plates compromise both sealing and pressure capability.
How to bridge them
- Adapter flange: A purpose made flange with one face to ASME and the other to EN
- Spool piece: A short pipe section with a different standard flange at each end
- Change the equipment side: Convert the pump or valve mating flange to the project standard
A spool piece is usually the cleanest answer; it creates a clear boundary between the two systems and simplifies later maintenance.
When ordering
State standard, class (Class or PN), type and face form together. On metric projects, remember that studs and nuts must also be metric; a metric nut does not fit an ASME stud.
Our dimension tables cover both standards: flange page. Send your list through the enquiry form.
FAQ
Are PN 16 and Class 150 the same?
No. Their pressure temperature behaviour and bolt circles differ, so they are not interchangeable.
How are the two standards joined?
With an adapter flange or a spool piece carrying a different standard flange at each end.
Which studs go with metric flanges?
Metric ISO threaded studs and nuts, never mixed with imperial threaded items.
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